New research: Leptospira bacteria now also found in brown rats in Sweden

News 19-11-2015 11:59

A new study conducted by Uppsala University in close collaboration with Anticimex has been published. In the study, rats in people’s immediate vicinity in three major Swedish cities have been examined.

For the first time since the 1930’s, researchers have found rats that carry antibodies against the most serious subtype of Leptospira, a bacteria that can cause serious illness in humans. However, Leptospira is not unique to Sweden. Reports from other countries such as Denmark, Ireland, Portugal and Germany also show that Leptospira could be on the rise in Europe.

Statistics show that the number of rodents is increasing in Sweden. At the same time, there is a lack of knowledge regarding which microorganisms our native rats are carrying that can cause illnesses in humans. Therefore, a research team at the Zoonosis Science Center, IMBIM, at Uppsala University, has been conducting a research project to identify which infectious microorganisms Swedish rats could transmit to humans.

A total of 30 rats from Stockholm, Gothenburg and Malmö were analysed for Leptospira antibodies using the recognised method MAT (Microscopic Agglutination test). The rats have been collected by Anticimex from people's immediate vicinity such as apartments, cafes and shopping centres.

– We began by searching for Leptospira, a bacteria found in 300 different variants, several of which can be very dangerous for humans, says Tanja Strand, researcher at the Zoonosis Science Center at Uppsala University.

13 percent of the analysed rats were tested positive for the most severe variant of the Leptospira bacteria, Leptospira interrogans serovar Icterohaemorrhagiae. The bacteria can, in the worst cases, lead to meningitis or leptospirosis, often called Weil's disease. Weil's disease has a mortality rate of five to ten percent.

– In modern times, there have only been occasional patients infected with Leptospira in Sweden. This new discovery in rats could indicate that leptospirosis is on the rise in Sweden, says Tanja Strand.

Leptospira is, however, not unique to Sweden. Reports from countries such as Denmark, Ireland, Portugal and Germany also show that Leptospira could be on the rise in Europe. One report from Denmark showed that 63 percent (74 people) of 118 patients infected with Leptospira developed Weil’s disease, of which 7 percent (5 people) died as a result of the illness.

– The fact that carriers of Leptospira are among us is new and troubling knowledge, says Thomas Persson Vinnersten, biologist at Anticimex. Furthermore, statistics show that the number of rodents is increasing, and they are also becoming more resistant to rodenticides. This makes urgent demands on future pest control methods.

Together with Anticimex, the research team at the Zoonosis Science Center will now expand their research, in order to include more rats from more cities and to search for other rat-borne infections than Leptospira. The goal is to continue exploring how large a threat native rats are to public health.

– In order to reduce the risk of people being affected by serious diseases, it is important to increase the awareness of the rats’ ability to spread pathogens, and to find effective methods to reduce the risk of infection, concludes Thomas Persson Vinnersten.

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